The present invention relates to a device for magnifying displacement of a piezoelectric element and a method of producing same, particularly for use with a printing head. The present invention also relates to a printing head including such a displacement magnifying device.
FIG. 37 shows a prior art device for magnifying displacement of a piezoelectric element 101. Referring to FIG. 37, a movable member 105 is attached to the piezoelectric element 101. On the other hand, a pair of leaf springs 106 and 107 are fixed at their respective one end portions to a frame 102 and the movable member 105, and a rocking block 108 is fixed to the other end portions of the leaf springs 106 and 107. When the piezoelectric element 101 is expanded upon application of voltage thereto, the movable member 105 is displaced to flex the leaf springs 106 and 107. As a result, there is generated a moment in the rocking block 108 to rock the same. Further, an elastically deformable connecting member 104 is fixed between the movable member 105 and a lateral projection 103 of the frame 102, so as to displace the movable member 105 in parallel to a direction of displacement of the piezoelectric element 101. However, it is hard to balance a spring force of the connecting member 104 to a spring force of the leaf springs 106 and 107, causing inclination of the movable member 105 relative to the direction of displacement of the piezoelectric element 101. As a result, an amount of flexing of the leaf springs 106 and 107 is fluctuated, and the rocking block 108 cannot be rocked at a desired rocking angle.
Such a problem has been intentionally eliminated by providing a quadri-hinged parallel link mechanism consisting of a pair of separate link plates 117 as shown in FIG. 37. Each of the link plates 117 is integrally formed with a pair of vertical link portions 118 and 119 and a pair of horizontal link portions 120 and 121. The vertical link portions 118 of the pair of link plates 117 are fixed to opposite side surfaces of the frame 102, and the vertical link portions 119 are fixed to opposite side surfaces of the movable member 105, so as to ensure parallel displacement of the movable member 105.
The leaf springs 106 and 107 are fixed by brazing to opposed surfaces of the frame 102 and the movable member 105. To improve the fixation of the leaf springs 106 and 107 to the frame 102 and the movable member 105, the leaf springs 106 and 107 are so disposed as to project laterally from the opposite side surfaces of the frame 102 and the movable member 105. Accordingly, when the link plates 117 are fixed to the opposite side surfaces of the frame 102 and the opposite side surfaces of the movable member 105, the horizontal link portions 120 and 121 of the link plates 117 interfere with the side projections of the leaf springs 106 and 107. To eliminate the interference, it is necessary to cut the side projections of the leaf springs 106 and 107 (as shown by a hatched portion). However, cutting of the hatched portion of the leaf springs 106 and 107 is difficult and requires much time and labor. Further, such cutting causes a reduction of the strength of fixation of the leaf springs 106 and 107.
FIG. 38 shows another example of the prior art device. When the application of voltage to the piezoelectric element 101 is cut to contract the piezoelectric element 101 to its original condition, the leaf springs 106 and 107 and a rocking arm 110 fixed at its one end to the rocking block 108 are returned to the original condition. At this time, the rocking arm 110 tends to be retracted more than the rest position by the inertia, and the leaf springs 106 and 107 are oscillated as shown by arrows P and Q by the elastic force thereof until stopped at the rest position. Accordingly, a time required for stopping the leaf springs 106 and 107 becomes long to hinder a high-speed rocking motion of the rocking arm 110 in response to the displacement of the piezoelectric element 101. Further, there is generated elastic fatigue of the leaf springs 106 and 107 due to the above-mentioned oscillation which reduces the durability of the leaf springs 106 and 107. To solve this problem, a stopper 135 is fixedly provided on an upper end of the connecting member 104 in opposed relationship to a lower longitudinal edge of the rocking arm 110. However, as the stopper 135 abuts against a substantially longitudinally central portion of the rocking arm 110, a free end portion of the rocking arm 110 tends to be flexed as shown by a chain line. Simultaneously, there is generated a moment in the rocking arm 110 about the stopper 135 to cause the oscillation of the leaf springs 106 and 107 in the directions of the arrows P and Q and the oscillation of the rocking arm 110 in the directions of arrows A and B.
Further, when the movable member 105 is returned to the original condition, the return motion tends to be delayed because of the inertia of the movable member 105, the leaf springs 106 and 107 and the rocking block 108. As the movable member 105 is fixed to the upper end surface of the piezoelectric element 101, a tensile force is applied to the piezoelectric element 101 because of such a delay. The piezoelectric element 101 is normally formed of piezoelectric ceramic having a weak property against the tensile force. Therefore, the piezoelectric element 101 tends to be damaged by the tensile force.
Referring back to FIG. 37, a pair of wedge members 141 and 142 are interposed under pressure between the lower end surface of the piezoelectric element 101 and the lateral projection 103, so as to apply a compression load to the piezoelectric element 101 and thereby ensure sufficient transmission of the displacement of the piezoelectric element 101 to the movable member 105. The upper wedge member 141 is fixed by adhesive to the lower end surface of the piezoelectric element 101, and the lower wedge member 142 is forced into a space between the upper wedge member 141 and the lateral projection 103, thus applying the compression load to the piezoelectric element 101. However, contact surfaces 141a and 142a of the wedge members 141 and 142 are required to be machined with a high accuracy, so as to ensure uniform application of the compression load to the piezoelectric element 101. Further, the number of parts is increased, and the assembling is rendered troublesome to cause an increase in cost.
FIGS. 39 and 40 show a prior art printing head. A plurality of printing units 201 (one of which is shown for simplicity) are inserted in a plurality of slits 203 formed in a substantially cylindrical holder 202 and arranged at circumferentially equal intervals. A flexible printed wiring board 206 having a plurality of connection terminals to be connected by soldering or the like to lead wires 205L of piezoelectric elements 205 of the printing units 201 is mounted on end surfaces of frames 204 of the printing units 201 on the side opposite to the holder 202. A cover plate 208 having a nose 107 for reciprocably guiding a plurality of printing wires connected to the corresponding printing units 201 is fitted with the holder 202.
In the event that any one of the printing units 201 is required to be exchanged because of breakage or wear of the corresponding printing wire, it is necessary to disconnect the lead wires of all the printing units 201 from the connection terminals of the flexible printed wiring board 206, and then remove all the printing units 201 from the slits 203 of the holder 202. Thus, the exchange of the printing unit 201 is very troublesome.